Telescopic cylinder assembly



April. 14, 1953 R. H. PTAK i TELESCOPIC CYLINDER ASSEMBLY 3 Sheets-Sheet l Filed Feb. 2l, 1951 INVENTOR.

.armen/5y R. H. PTAK TELESCOPIC CYLINDER ASSEMBLY April 14, 1953 Filed Feb. 21, 1951 3 Sheets-Sheet 2 INVENTOR. 1 RYMOND H PF4/f April 14, 1953 R. H. PTAK 2,634,587r

TELESCOPIC CYLINDER ASSEMBLY Filed Feb. 21. 1951 sheets-sheet 5 Fic-@.10

INVEN TOR.

Raymond H.Pcak BY,

Aorneys Patented Apr. 14, 1953 TELESCOPIC CYLINDER ASSEMBLY Raymond H. Ptak, Cleveland Heights, Ohio, as-

signor, by mesne assignments, to The New York Air Brake Company, New York, N. Y., a corporation of New Jersey Application February 21, 1951, Serial No. 212,015

Claims.

This invention relates to telescopic cylinders and will be described as embodied in a two-stage cylinder for fork lift trucks. It is adaptable to other uses.

The development of telescopic masts and telesc'opic lift motors has led to the production of fork lift trucks low enough to enter the side door of a box car and capable of lifting goods from oor level to levels which are well above the nor- 'mal height of the lift structure.

The present invention provides a motor Which is smaller in over-all diameter than motors of the prior art of equal lifting capacity; which has only one stuffing box instead of the usual two or more; and in which the bearings which maintain alinement of the telescoping units are favorably located and, with one unimportant exception, have no other function. Similarly, no packed .joint has even a secondary guiding function. Thus' the bearings and the packings can be designed and located each for its one function without compromise; better fits are commercially possible; rigidity is improved; servicing is rendered comparatively simple, and the life of the whole unit is increased.

To attain these desirable results, use is made in that portion of the device heretofore subject to particularly damaging bending moments, of an annular piston, and a thrust sleeve to which the piston is not connected but through which it delivers its lifting force. The piston carries its own packing. The thrust sleeve has its own bearings. The bearings absorb the bending mo-v ments exerted on the sleeve, and the piston being free, is protected from destructive stresses.

An incidental advantage is that the total area of the annular piston is effective, from which ows the fact that for a given lifting capacity the outside diameter of the hoist can be smaller than is practicable with conventional constructions.

These principles are applicable to telescopic units of specifically different forms, a preferred one of which will now be described by reference to the accompanying drawings.

In the drawings:

Fig. 1 is a longitudinal axial section of the complete hydraulic lift unit in collapsed condition. Parts are broken away to reduce the overall length of the view.

Fig. 2 is a longitudinal axial section of the :secondary plunger, i. e. the plunger which affords the second stage of lift.

Fig. 3 is an axial section of the cylinder unit, comprising the cylinder for the secondary plunger., and the encircling annular cylinder for the annular free piston forming part of the primary lift unit.

Fig. 4 is a longitudinal axial section of the thrust sleeve of the primary lift unit.

Fig. 5 is a longitudinal axial section of the free annular piston which works in the annular cylinder of Fig. 3 and delivers thrust through the thrust sleeve of Fig. 4. The piston packing is included in the View.

Figs. 6 and 7 are views similar to Fig. 1, Fig. 6 showing the parts at the end of the rst stage of lift, and Fig. 'Z showing the parts at the end of the second stage of lift. In Figs. 6 and 7 parts are broken away, to reduce the lengths of the views.

Figs. 8, 9, and l0, show how the improved lift unit is incorporated in a fork lift truck, not the invention of the present applicant, and for which the illustrated embodiment of the invention was developed.

It is characteristic of the invention that two ,coaxial nested open-ended cylinders are arranged with their respective open ends oppositely directed. Each cylinder contains a plunger which is projected from the open end to perform a part of the hoisting operation, and the two plungers function serially despite the fact that they are simultaneously connected to a common source of pressure iiuid. The effective area of one plunger is greater than that of the other, and the loads to which they are subjected though different, are not sufficiently different to neutralize the effect of this difference of area.

The basic components will rst be described by reference to Figures 2, 3, li, and 5, after which the assembled relations of the parts will be described and the mode of operation set forth.

Figure 2 shows the secondary plunger i8, i. e. the plunger which has the smaller effective area and operates last. It comprises a tube 20 open at its upper end, and closed at its lower end by a head piece I8 which is welded to the tube. The head piece has an eye I9 by which the plunger may be hinged to the base of a lift truck. Near its upper end the tube 2B is encircled by a stop ring 22 which is fixedly attached to the tube. The upper end of the tube is reduced in external diameter to receive an encircling bearing ring 24 which is removably retained by means of a snap ring 26. As shown on the drawing, the ring 26 engages in a groove formed in the reduced portion of the tube to receive it.

The pressure liquid for operating the hoist is communicated through a connection attached to the threaded opening 28, which communicates with the bore of the tube 20. Immediately below the stop ring 22, ports 32 are formed through the tube 28.

The cylinder unit i2 is made up of two coaxial tubes 3-6 and which are connected at their lower ends by a ring 48 which is welded to the larger tube 58 and also welded to a tubular hub member 3i'. which forms an extension of the smaller tube 35, being welded thereto. Immediately above the ring :i8 the hub is formed withy through ports S2. The smaller encircled tube 35 is much longer than the encircling tube '59', and is closed at its upper end by a head 38 welded in place. A bleeder port in head SS is normally closed by a threaded plug 6d'.

The hub 34 is counterbored to form a gland to receive packing 4Q, and this packing is held in place by combined bearing and follower ring 42 which is engaged by thegland nut 44, threaded into the lower end of hub 34. A wiper ring 4B is associated with the gland nut 4d. The ring 42 is rigidly sustained by hub 34 and affords a satisfactory bearing for plunger I6 despite the fact that it also serves as a follower ring for the packing.

The bearing 24 on the plunger i!! fits the bore of the tube 3S and the tube 20 proper ts the bore of the combined follower ring and bearing 42. The exterior of the tube 20 is machined and both the interior and the exterior of the tube 36 are machined.

A removable stop ring 54 with wiper ring' 58 is mounted in a counterbore formed within the upper end of the tube 58 and is retained by a snap ring 56. The annular space 83 enclosed between the tubes 36 and 50 serves as the working space of the primary hoist.

Plunger i4 of the primary hoist is shown in Figure 4. It comprises a tube 66 to which is welded at its upper end a tubular extension 58.

The internal and external diameters of extension S8 are less than the corresponding dimensions of the tube 56. The effect being to form an internal stop shoulder 65' and an external shoulder 51 against which a trunnioncarrying member 38 forming part of the lift truck, may be mounted. When so mounted it is retained by the snap ring 69.

A stop ring 'l0 is fixed at thelower end of the member Hi and encircles it. This ring 1B coacts with the ring 54 to limit projection of the plunger id. Mounted in a counterbore in the lower end of the tube 66 is a removable bearing 'l2 which is retained by a snap ring 14. Another bearing ring 76 is permanently mounted within the extension E8. The two rings are nearly at the opposite ends of plunger M, have the same internal diameters, and make close sliding ts with the exterior of the tube 36. A wiper ring 78 is mounted within the upper end of the extension member B8.

The member I4 is guided on the exterior of the tube 35 and telescopes into the working space 86 in the cylinder member. At' its lower end it is in thrust engagement with the annular piston EB which is a floating piston. Piston i (as best shown in Fig. 5) comprises an annular metal core 8e, T-shaped in cross section, its form affording internal and external recesses for the packing rings S2 and 8d respectively. The packing is retained in place, as clearly shown in Figure 5, by ordinary removable follower rings held by snap rings. As best shown in Figures 1, 6, and 7, these follower rings have no rubbing engage- 4 ment with the tubes 50 and 36 of the cylinder unit l2 and the same is true of the core 30.

The floating piston IE works in the annular cylinder space 86 and when forced upward by pressure fluid forces the sleeve is upward. Pressure fluid admitted through the connection 28 enters the bore of the tube 2t and reacts upward on the head 38 xed in the upper end of the tube 3e. It also flows through the ports 32 into the interval 64 between the tube 2t and the tube 36. From the space 6l! it flows through the ports 62 intothe space 8B beneath the floating piston It. Except to the slight extent that resistance to flow between the two working spaces of the hoist creates a pressure differential, these Working spaces are always at the same pressure.

A breather 52 of. conventional form connects the space above piston It freely with the atmosphere. Y

The parts are assembled as clearly shown in Figures 1, 6 and 7. Plunger lil is accurately guided in the tube 36 of the cylinder assembly I2 by the bearing ring 2li at its upper end, and by the combined bearing ring and follower [l2 at the lower end of the cylinder unit. The two bearings are quite widely spaced apart at their closest approach, which occurs, as shown in Figure 7, when the stop ring 22 engages the upper end of hub 34.

The plunger sleeve le slides on the exterior of the. cylinder tube 3S and is guided thereon solely by the bearings 'i2 and 'it carried by the sleeve. These are spaced apart nearly the length of the sleeve lll. Consequently good alinement is assured. The piston l can be loaded only in thrust. Its packing seals against the nished exterior of tube 36 and against the finished interior of tube 50. Outward motion of the sleeve I4 is limited by the collision of stop ring 70 with stop ring 54. When the sleeve is arrested the piston I6 is also arrested.

Contraction of the hoist ends when the upper end of plunger l@ engages the head 33 and the lower end of sleeve I4 forces the piston it into contact with the ring 48 of the cylinder unit l2.

There is only one packing gland, namely the glandV which receives the packing de. The gland nut and related parts are accessible. Removal of ring 5d permits withdrawal of the plunger sleeve M and the piston i6 from the cylinder unit, in case it is necessary to replace worn packings.

With the parts. constructed asv above described and proportioned substantially as shown in the accompanying drawing, the eifective area of piston i6 is approximately twice the efective area of the secondary plunger lli. The effective area of plunger lil corresponds to the outside diameter of the tube 2B. The ratio of the two eiective areas mentioned can be selected to meet the requirements of particular installations, and this permits adaptation of hoists embodying the invention to a considerable range of uses.

Solely as a basis for explaining. the principles underlying the invention, the hoist is shown in Figures 8-10 as applied to a telescopic forklift truck. rhe particular embodiment shown in Figs. l-7 was designed for this particular use.

The body of the truck is indicated at A and the front wheels at B. The truck carries a fixed frame which comprises a sill member C slightly above the oor level, and two channel uprights D which are parallel, and which are tied together at the topby anV offset cross member E. vertically guided by the uprights D is a movable frame comprising substantially vertical side members F and a cross yoke G which connects the side members F. Guided for vertical movement on the movable frame FG is the lift fork H. The guiding means for the lift fork H are not elaborated since they would confuse the drawing and in any event are conventional.

The hoist above described is mounted with the eye I9 of its secondary plunger Il) hinged to the sill member C and the head 38 of the cylinder member 36 connected with the cross yoke G of the vertically movable frame.

The trunnion-carrying member 38 shown in Figures 1, 6 and 7 carries at each of its ends a corresponding one of two coaxial sprockets K,

over which are trained corresponding ones of two chains L. Each chain L is connected at one end to a corresponding one of two brackets M on the fork unit H and at its other end to a corresponding lug N. These lugs are mounted on opposite sides of the cylinder unit I2.

When pressure fluid is admitted to the connection 28 (see Fig. 2), it develops two force reactions Which are opposite and of different magnitudes. Each of these can best be considered as relative to the dual cylinder unit I2.

The larger force reaction is between cylinder unit I2 and annular piston I6 and causes the piston I6 to move full stroke upward before the smaller downward force reaction produces any motion. The piston reacts upward through sleeve I4 upon member 83. The sprocket and chain rig multiplies the motion of sleeve ill by two, and so causes the fork H to move from door level (see Fig. 8) to the top of the movable frame FG, i. e., twice the travel of piston l5. The frame FG remains in its lowermost position (see Fig. 9). Piston IS thus operates at a mechanical disadvantage in the ratio of 2 to l with respect to the lift fork and its load.

When piston I6 has moved full stroke and is arrested, the second force reaction which is between cylinder unit I2 and plunger it becomes effective and causes the cylinder unit to rise and lift frame FG relatively to frame DE. The extreme upward position is shown in Fig. l0.

It will now be clear why the effective area of piston I6 is made approximately twice that of plunger i0. The precise ratio used takes account of the fact that the second force reaction must lift the initial load augmented by the weight of cylinder structure I2, frame FG and related parts. Friction, both mechanical and hydraulic, is a disturbing factor, the amount depending on the particular design.

Ideal proportioning assures that in the lifting cycle piston I6 will move full stroke before plunger I6 starts to move and in the lowering cycle plunger I will complete its inward stroke before piston I6 starts to move inward. In each cycle transition between the two phases of motion must be smooth, and smoothness of transition in the lifting phase is probably the more important where compromise is necessary.

As a practical matter there must be a slight differential between the pressure when piston I6 ends its lifting stroke and the (higher) pressure necessary to start plunger i0 on its lifting stroke. This dierential should be large enough to assure strict serial action in -both directions, but not so large as to cause jerky action.

Figures 8-10 illustrate simply one environment in which the hoist may be used. The approximate 2 to 1 ratio is a function of the 2 to 1 6 motion ratio characteristic of the sprocket and chain rig. Obviously the invention will afford (within limits) any ratio (including 1 to l) that a particular environment may make desirable.

Many diiferent arrangements of telescopic lift trucks are known and the invention is not directed to a truck, but to a hoist motor suited for use in such trucks.

What is claimed is:

l. In a lift motor, the combination of a housing enclosing two coaxial cylinders separated by a cylindrical wall whereby one cylinder is annular and encircles the other, each cylinder having one closed and one open end, said cylindrical separating wall extending from the closed end of the encircling annular cylinder through, and beyond the open end thereof for a substantial distance, the outer surface of said wall being formed as a longitudinal guide; a thrust sleeve encircling said wall and having at its outer end a bearing coacting with the guiding portion thereof, the inner end of said sleeve extending into said annular cylinder and having near the inner extremity thereof a bearing coacting with at least one of the cylindrical walls of said cylinder; a free annular piston reciprocable in said annular cylinder defining therein a working space and adapted to react in thrust against the inner end of said sleeve; plunger means reciprocable through the open end of the encircled cylinder and defining another working space therein: and connections for admitting and exhausting pressure fluid to and from both said working spaces.

2. In a lift motor, the combination of a housing enclosing two coaxial cylinders separated by a cylindrical wall whereby one cylinder is annular and encircles the other, each cylinder having one closed and one open end, the open ends being op-positely directed, said cylindrical separating wall extending from the closed end of the encircling annular cylinder through, and beyond the open end thereof for a substantial distance, the outer surface of said wall being formed as a longitudinal guide; a thrust sleeve encircling said wall and having at its outer end a bearing coacting with the guiding portion thereof, the inner end of said sleeve extending into said annular cylinder and having near the inner extremity thereof a bearing coacting with at least one of the cylindrical walls of said cylinder; a free annular piston reciprocable in said annular cylinder defining therein a working space and adapted to react in thrust against the inner end of said sleeve; a plunger reciprocable through the open end of the encircled cylinder; bearings spacing said plunger from the walls of its cylinder, one bearing encircling the inner end of the plunger and carried thereby and the other supported .by the cylinder adjacent said open end; a packing ring carried by the cylinder and sealing against the plunger between said bearings, whereby a working space within the encircled cylinder is defined; and connections for admitting and exhausting pressure fluid to and from said working spaces.

3. In a lift motor, the combination of a housing enclosing two coaxial cylinders separated by a cylindrical wall, whereby one cylinder is annular and encircles the other, each cylinder having one closed and one open end, the open ends being oppositely directed, said cylindrical separating wall extending from the closed end of the encircling cylinder through and beyond the open end thereof for a substantial distance to the closed end of the encircled cylinder, the external surface of said wall being formed to serve, as. a longitudinal guide; plunger means reciprocable through the open end o f the. encircled cylinder and denng therewith aworking space; a thrust sleeve longitudinally guided by said Wall and extending into the open end of said annular cylinder; a, f-ree annular piston recprocable in said annular cylinder, dening therein another working space and adapted to react in thrust against said sleeve; and connections for admitting and exhausting pressure fluid to and from both said working spaces.

4. The combination dened in claim 3 in which said plunger means is guided in the encircled cylinder by two bearing rings which space the plunger from the cylinder, one ring carried 15 Number by the plunger and thel other by the cylinder;y

and a stung box is mounted in the open end of said cylinder and seals the plunger.

5. The combination dened in claim 2 in which the sleeve carries spaced bearing bushings each of which engages said guiding Wall; and said free annular piston is provided with internal and external packing rings.

RAYMOND H. PTAK.

References Cited in the le of this patent UNITED STATES PATENTS Name Date Re. 7,438 Van Emon Dec. 19, 1876 

